A production method having a multiplicity of punches arranged in a row is known from DE 4 334 203 C2. In that patent, there are embodiments with two dies to be introduced into the tube, which dies together fill out the tube cross section. Other embodiments in the cited document use only a single die which likewise fills out the entire tube cross section. In the case of the production of the slots by means of a single die, it is provided that, after the formation of the slots, the die is rotated through 180° out of the working position into a refracted position in order that the die can be removed from the tube again. Realizing large rotational travels, however, can have an adverse effect on the cost-effectiveness of the manufacturing process, because longer cycle times could be necessary. Also, to be able to realize adequately large collars on slot edges, the die disclosed in DE 4,334,203 C2 has, between its axially arranged supporting portions, axial connecting portions of relatively weak form (connecting portions—see FIG. 7, reference no. 4 in DE 4 334 203 C2). Cracks may therefore form in the die. Furthermore, DE 4 334 203 C2 discloses only circular tubes. However, it is desirable to be able to provide tubes of as wide a variety of cross-sectional shapes as possible with the slots.
U.S. Pat. No. 5,088,193 A also relates to the slotting of circular tubes and the use of an inner die. Here, by contrast to DE 4 334 203 C2 cited above, there is not a multiplicity of punches arranged in a row. By contrast, in U.S. Pat. No. 5,088,193 A, it is provided that, firstly, in first working steps, embossings are formed in the tube wall by means of an arcuate punch corresponding to the tube contour. In the tube there is situated the die, the cross section of which is only slightly smaller than the inner tube cross section. The die is subsequently removed from the tube, and in second working steps, the slots are formed in the embossings by means of a piercing tool. A rotational movement of the die is not necessary, because said die is in the form of a continuous circular bar without supporting and connecting portions. There is nevertheless a disadvantage at least with regard to the cost-effectiveness of the manufacturing process. Also with regard to U.S. Pat. No. 5,088,193 A, a pressing tool is used for the first steps and a slotting or piercing tool is used for the further steps, which can be regarded as being disadvantageous.
In the production of slots as described above, basically no cuttings are produced as waste, whereby said methods are distinguished from other known methods in which holes are firstly cut out and the hole edges are subsequently bent into the form of flanges.
In other known applications, tubes to be slotted are filled with a liquid in order to support the tubes from the inside during the production of the tube slots.